The goal of this project is to determine whether chronic pretreatment with different classes of the newer antiarrhythmic agents, influence the nature and frequency of ventricular arrhythmias following coronary occlusion in the closed-chest conscious dog, -and whether the effects of these agents on arrhythmias can be correlated with their electrophysiologic actions on the ischemic myocardium in relation to their serum and tissue levels. The -arrhythmias will be recorded continuously on Holter tapes which will be analysed at 60X real time using computer techniques; the electrophysiologic characteristics of the ischemic myocardium will be evaluated using intracellular microelectrode techniques - and gas liquid chromatography will be used to determine the serum and tissue concentrations of different antiarrhythmic agents.